Rise to the situation when you fall off a horse (7)
I believe the answer is:
'horse' is the definition.
(remounting is a kind of horsing)
'rise to the situation when' is the wordplay.
'rise' becomes 'mount' (both can mean to increase).
'to' means one lot of letters go next to another (I've seen this in other clues).
'the situation when' becomes 're' (I can't explain this - if you can you should believe this answer much more).
'mount' put after 're' is 'REMOUNT'.
'you fall off a' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for remount that I've seen before include "Get back on a horse", "stage again".)